text:
How to calculate g load from max lift coefficient?
I calculated for my flight configuration for different angle of attacks (0° to 20° in pitch) the corresponding lift coefficients for my aircraft (horizontal flight, only pitching).

I would like to know how I can now calculate the maximum load factor I can fly a curve in the horizontal? I would like to do the turn by rolling to a certain bank angle.

Example: when I calculate from question 1. let us say 2 g - this means a bank angle of approx. 60°. What happens if I roll to 65°, will the nose pitch down because I do not have enough lift anymore?

Can I accelerate my angular velocity while let us say banking to 20° and then pulling control stick (in pitch) ? So this is what I remember from flight simulator that I can turn more quickly when I bank and then pull the stick. Or will I also need more lift for this?

Could you please help me in this?
Thank you
Lucas

For number 3, please specify, are you A) no longer constraining the flight path to be horizontal (suggested edit: "The flight path need not remain horizontal during this maneuver"), or B) still requiring the flight path to be horizontal (suggested edit "Can I accelerate my angular velocity, while still keeping the flight path horizontal, while let us say banking to 20 degrees and then pulling control stick (in pitch)?)"   Without knowing this, it's tough to give a meaningful answer.

maximum load factor I can fly a curve in the horizontal

Will always be 1/cos bank angle. Cos 60 degrees = 0.5 G load = 2G
You are touching on the "accelerated stall" concept.  You can pull more Gs with more AoA (increasing Coefficient of Lift), or you can speed up and keep your AoA well below stall.  This is why we enter steep turns in a 172 at 90 knots, even though our (level flight) stall speed is around 50 knots.

if I roll to 65 degrees, will my nose pitch down

If you're lucky, yes, you will enter a spiral descent.  However, if your AoA is near stall, the outside aileron down wing may stall because it (locally) exceeded it's stall AoA.  If it does, immediately reduce pitch before recovering.

can I accelerate my angular velocity by banking ... and pulling on the stick.

As you bank, the elevator does do more and more of the "yaw" through the earth referenced level flying circle, but again minimizing airspeed and maximizing AoA (by pulling the stick) can lead to an accelerated stall.

I’m going to constrain the possible answers by stating a couple of assumptions that are standard in this sort of example:  That you are making a level turn, and that you are keeping airspeed constant.
Question 1:  The maximum load factor is a function of the structural strength of the aircraft.  You can calculate what it is at varying angles of bank or reference a chart, but either way your limit will be published by the manufacturer as G limits, and is expected to be known by you the pilot.  Therefore, instead of calculating your max load factor, you will know your max load factor and can then calculate your max AOB for a level turn.
Question 2:  If you do not change anything else then yes, the nose will start to drop and you will descend when you increase AOB.  However, this is easily countered with additional power and backpressure to maintain altitude and airspeed.  Interpolating the graph below, a 65 deg AOB turn would require approximately 2.5 Gs to maintain altitude.
Question 3:  At very steep knife-edge turns, or in a vertical or orthogonal plane, yes.  But if you are holding a constant 20 degrees AOB turn and then increase pitch you will simply begin a climbing turn because most of your lift vector points upwards.  The only way to increase angular velocity and tighten your turn radius in the horizontal plane is to increase angle of bank and adjust pitch proportionally to maintain altitude.  (i.e. get your lift vector pointed in the direction you want to turn and load up the Gs, or "roll and pull...")  More power will be required to overcome the additional induced drag and maintain airspeed.
This isn’t a complete tutorial on what makes an airplane turn, but there is plenty of information on this site and in other places that break down and explain the horizontal and vertical components of the wing’s lift.  When combined with the chart below this should help you gain a better understanding of the relationship between AOB, G forces and turn performance, and get clarity on your questions.


text:
Variable-pitch propeller blade design (AOA)
For a variable pitch propeller where the angle of attack can be adjusted during flight, are the individual blades similar in design to standard propellers, with a low angle of attack at the edge of the propeller (3-6 degrees), and gradually increases towards the root (14-16 degrees); or are the propeller blades one singular angle of attack throughout the entire length of the blade?
I'm presuming the blades have a differing angle of attack at the root and tip, but of a lower magnitude to prevent the root AOA exceeding the critical angle?

All aircraft propeller blades are designed with a varied angle between the hub and tip because the tips are turning faster than the hub. The Wright Brothers were the first to figure it out sometime around 1902.

Are you asking if the root-to-tip difference in blade pitch is less on a variable pitch prop than on a fixed pitch prop?  (Other respondents so far seem to have fixated (heh) onto "one singular AoA throughout the entire length.")

A couple of important distinctions here:

Angle of Attack (AoA) is the local angle of the blade profile relative to the airflow.
Blade pitch is the local angle of the blade profile relative to the propeller rotation axis
Variable pitch propellers can offset the whole blade with an additional angle. The shape of the blade will remain constant.

Picture above is from this link, which contains a good explanation on propeller blade shapes. It shows the AoA, with the two velocity components Relative Wind and Rotational Velocity. And the Rotational Velocity increases with increasing local blade radius. So in order to have a constant local AoA at every point of the blade, the local blade pitch must be a (linear) function of distance from the centre. Which can be seen in all propeller designs, old and new, fixed blade or variable pitch.
Pic source
The term Variable Pitch may cause some confusion. All propellers have a local profile pitch angle relative to the spinning axis that changes with local radius, like in the pic above. But Variable Pitch means: the whole blade can increase its pitch angle, to keep the AoA constant with increasing airspeed.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
Is MIL-STD-1553 still used in modern aircraft?
I am working on an assignment for my "Avionics Systems Design" class and I want to use MIL-STD-1553 for my aircraft system. But according to some shady blogs this STD has been deprecated or superseded by MIL-STD-1773.
If I don't want to use an optical solution, what is the best bus for my system?

According to Wiki, 1773 is 1553 with fiber physical layer, so strictly speaking it doesn't "supersede" 1553. It's more like a variant that has its own application, e.g. EMP resistance, longer transmission distance and higher data rate. Also, I really don't think fiber so prevalent on airplanes now that the copper version doesn't exist at all so the answer to your question is probably yes? Also in your assignment you probably care about logic than physical so why care?

MIL-STD-1553 buses have too low data rate, leading to multiple parallel buses to support peak data rates, hence the 1773; at least as far as I understand the history of these two. Also check SAE AIR4508A if you have access, it provides some background on the two specs you mention.

Are you wanting to design a system for military applications or civil applications? What size aircraft?

Your instructor has given you the materials you need to do the assignment, and thus won't mind if you ignore advice from blogs that you've already figured out are untrustworthy.

I can say 1553 is still used.  I'm not allowed to say more. ;)

MIL STD 1553 is alive and still in use.  Backwards compatibility will keep it around for some time.  Not only is it used in aircraft but also on spacecraft.
It tends to be used for control applications and lower data rates.  High volume data, for example from sensors, will employ different bus structures.  Many control, communications and guidance applications can readily be accomplished with 1553.
Having said that, I cannot say whether it is right for you application, as I know little about your application.  Noise, data rates, latency and other factors may cause you to look at different interconnection architectures. There are many competing bus/LAN structures.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Can i create a home built aircraft with this engine?
http://www.chiefaircraft.com/da-100.html
Would this engine work for a homebuilt ultralight aircraft? I am still in the research phase, so i don't know what the weight of the aircraft will be, but I would like to know what a good prop size and max weight that it will be able to fly.

It's a 100cc engine, and it's in the Radio Control section of that web site. It's an engine for model aircraft.
I suppose, technically, that's a home-built aircraft, but you're not going to sit in it!

Sure, people have sat in airplanes made mostly from radio control parts.  http://inspire.eaa.org/2018/07/27/foam-airplane-from-ohio-makes-world-debut/

You can use any engine in a homebuilt or ultralight, including one from a Model A Ford  if you want.  A 10 hp RC engine that runs at 8000 rpm?  Even if you were building a single seat ultralight, in most cases you'd need at least 3 to 4 of them to have any kind of decent performance, if you could stand the racket they make.  For something that can carry two people, 5 or 6 at least.
You'd have a pretty cool looking bank of throttles to control all those motors though!
That being said, I can think of one practical application; a Lazair ultralight has probably one of the lowest power requirements in the ultralight business and got by on two 10hp 2stroke forestry water pump motors, so two of those RC motors on a Lazair, of which used ones are easy to find, should work.

Are they FADEC? Your flight engineer might need to be an octopus...

Scale up to the DA-150L, https://www.desertaircraft.com/products/da150l.  It's more mature and widely available.  With a 32x12" prop it gives 82 pounds of thrust at 5400 RPM.  It puts out 16 hp.  The "original ultralight" Easy Riser flew with just 11 hp.
So it's possible.  Here's some broader discussion of more than just the powerplant:
Can an ultralight aircraft fly with a 18hp engine?

Yes that one has potential.  You need your ultralight to be able to at least manage some sort of climb on 16 hp though. Otherwise the two engines just doubles the risks of an engine failure, with the remaining engine taking you directly to the scene of the crash as they say.  Two of those would make a Lazair quite a performer and it would likely do pretty well single engine to boot. It was pretty marginal on 10hp a side.

Desert Air makes R/C aircraft engines.  The 200 cc DA-200 puts out around 19 hp.  I would go with 3 DA-100, two on the wing, one on the nose, giving it the Ford Trimotor look.
But these engines run around $ 1000.00 US dollars each, and are NOT designed for human flight.
It may be possible to time share a safer aircraft such as a Cessna 152 at a local airport for that kind of money.
But if you wish to proceed, the single cylinder 2 cycle 313 cc 28 hp Hirth F-33 is specifically designed for ultralights, yet would pass for an R/C engine any day.
And please do not believe the Wright Brothers got by on 12 hp.  That version barely got off the ground.  Weight reduction, however, is helpful.


text:
Could the Aurora D8 have Ramjets instead of traditional jet engines?
By the  design of the Aurora D8, the engines would receive the boundary layer of air atop the fuselage, however, because jets have what I am calling "moving parts", and the pressure differences would cause problems for the turbines. Could we eliminate this factor with ramjet engines?

It would cause even more problems for rams.

Replacing the turbines with ramjets won't work.
If the airplane had ramjet(s), it would still need enough thrust from non-ramjet engines to reach about Mach 0.5, because ramjets can't accelerate from a standstill, and they make hardly any thrust below that speed.  See the Nord Griffon, for example.

The Aurora D8 doesn't have traditional jet engines at all. The design incorporates a very large bypass fan which due to its size is not mechanically linked to the engine core. It's more like a turbo-prop engine, but driving a ducted fan instead of a propeller. The fan is specifically designed to cope with the flow disturbance in the boundary layer. Indeed, according to the Wikipedia article

Clustering the engines together atop the wide tail of a flattened fuselage enables them to reenergize the slow-moving boundary layer over the fuselage

Take a look at that article. It might answer a few more of your questions.

Hi Rauligio and welcome to ASE.
As an answer to your question: no. As the Aurora D8 is designed to fly at subsonic speeds, and ramjets work most efficiently at supersonic speeds around mach 3, they simply would not be feasible on Aurora D8.


text:
How to calculate camber for a balsa glider?
I am making a rubber powered balsa glider for a competition. I want to make the glider fly as long as possible. I've heard that a high camber means slower speed means more airtime. I want to make sure that the camber isn't too high, and I need to know what type of camber I should use. Also, I need to know if the horizontal and vertical stabilizer size is fine.
The dimensions of my glider include: 32cm fuselage, 7.8cm wing chord, 28cm wingspan, 5.5cm horizontal stabilizer chord, 11.5cm horizontal stabilizer span, 5cm vertical stabilizer height, and 5.5cm vertical stab width.

It's a bit unclear. Are you optimising for flight duration or flight length ?

The problem here is that a catapult launched glider needs low camber during the launch and higher camber during the low-speed glide. Either you pick a compromise, or try to build a wing with flexible ribs that flattens out at speed (which is what the experts do).

Optimising for duration.  Optimising for distance traveled would have been phrased "as far as possible," not "as long as possible."

Welcome to Aviation SE, Samarth!
Flight duration depends not only on camber, but also launch speed, launch angle, mass, propeller diameter, propeller pitch, rubber quality, winding tightness, etc.  I assume that by "rubber powered glider" you mean rubber band powered for the first part of the flight, gliding thereafter.
Even if you somehow find optimal values for all the other parameters except for camber, it's still simplest -- and most trustworthy! -- to build several interchangeable wings for the glider, varying camber, and directly measuring flight duration with a stopwatch.


text:
Yaw rate of a multi-rotor
Is there any type of relation that limits yaw rate of a multi-rotor (i.e quadcopter)?
Something like this relation for fixed wing aircraft: $R = \frac{v^2}{g \tan(b)}$, where $R$ is the minimum turning radius and $b$ is the maximum bank angle.

note that that formula is for a coordinated turn. you might get a higher yaw rate if you remove this constraint. what kind of constraints are you interested in for your answer?

A conventional quadcopter yaws by speeding up two rotors and slowing down the other two.  Once those two have slowed down to zero RPM, it can't yaw any faster.
A formula for this would involve the rotational moments of inertia of each motor+rotor and of the quadcopter's chassis, and the distance from the quadcopter's center of mass to each rotor's axis.  (If the rotors aren't coplanar, it gets messy.)
If those two rotors can be reversed, then they are (inefficiently) thrusting up instead of down.  The limit then may be when they overpower the thrust of the first two, forcing the quadcopter to descend.  Or, if the rotors are spectacularly inefficient when reversed, the limit is when the rotors reach maximum RPM.

this is true for yawing without banking, but a quadrorotor can still turn like a fixed wing would do

But a coordinated turn yaws much slower than a pirouette, and yaw rate is what the question is about.  The coordinated turn formula is merely incidental.

it depends, I have worked with multirotors that have a pirouette faster than a coordinated turn, and ones that don't. they're not all the same


text:
The relation between Euler-angle rate and body-axis rates?
A
paper  about quadcopter dynamics and control
shows the relation between Euler-angle rate and body-axis rates as:

Q1: why are there $R_{v2}^{b}(\dot{\phi})$, $R_{v1}^{v2}(\dot{\theta})$, and $R_{v}^{v1}(\dot{\psi})$?
I understand these are rotational matrices, but how could we use the $\dot{\phi}$, $\dot{\theta}$ and $\dot{\psi}$ to replace $\phi$, $\theta$ and $\psi$?
Q2: is the eqn(7) the approximate representation of the relation between Euler-angle rate and body-axis rates?  if YES, what are accurate representation?

Let me use the following graph to try to clarify your confusion, which is excerpted from Etkins, Dynamics of Flight:

The body axis is rotated from the [flat] Earth axis via a series of Euler angle rotations, $\psi$ (heading), $\theta$ (pitch), $\phi$ (roll), in this sequence. In the nomenclature of the graph, we've rotated from the Earth axis: $(x_E, y_E, z_E)=(x_1, y_1, z_1)$ to the body axis: $(x, y, z)$.
Now angular velocity is always expressed in the body axis, so the roll rate $p$ is about $x$, the pitch rate $q$ is about $y$ and yaw rate $r$ is about $z$. Our goal is to relate an instantaneous change in Euler angles ($\dot{\phi}$, $\dot{\theta}$, $\dot{\psi}$) to the angular velocity ($p$, $q$, $r$). Since the rotation is instantaneous, it does not add to the existing Euler angles.
We start off backwards, with the last rotation, $\dot{\phi}$. This rotation is about $x=x_3$, which is the same unit vector as $p$. Therefore, no frame transformation is required. i.e. trivially $\dot{\phi} = p$. That's why your rotation matrix, $R_{v2}^b$, is identity.
Next, let's look at $\dot{\theta}$. This rotation is about the $y_3=y_2$ axis, which lags behind the body axis by a roll rotation ($\phi$). So to bring it to the body axis, we need to pre-multiply by $R_{v1}^{v2}=\begin{bmatrix} 1 & 0 & 0 \\ 0 & \cos{\phi} & \sin{\phi} \\ 0 & -\sin{\phi} & \cos{\phi} \end{bmatrix}$.
Last, $\dot{\psi}$ is about $z_2=z_1$, which lags behind by two rotations: $R_{v1}^{v2}R_v^{v1}=\begin{bmatrix} 1 & 0 & 0 \\ 0 & \cos{\phi} & \sin{\phi} \\ 0 & -\sin{\phi} & \cos{\phi} \end{bmatrix}\begin{bmatrix} \cos{\theta} & 0 & -\sin{\theta} \\ 0 & 1 & 0 \\ \sin{\theta} & 0 & \cos{\theta} \end{bmatrix}$.
When you add everything together, we have the kinematic relation:
$$\begin{bmatrix}p \\ q \\ r\end{bmatrix} = \begin{bmatrix}1 & 0 & -\sin{\theta} \\ 0 & \cos{\phi} & \sin{\phi}\cos{\theta} \\ 0 & -\sin{\phi} & \cos{\phi}\cos{\theta}\end{bmatrix} \begin{bmatrix}\dot{\phi} \\ \dot{\theta} \\ \dot{\psi}\end{bmatrix}$$
To answer your second question, no, this is not an approximation because the angular velocity is, by definition, an instantaneous change. Magic of calculus. The paper is incorrect to say that the rates are small; the magnitudes of the rates have no bearing on the derivation of the kinematic relation.

Your answer completely answered my doubts and thank you

+1 for a most comprehensive answer.

does this apply to any Euler convention or just a particular one e.g. 123 ?

is the matrix always invertible for all orientation?


text:
Are there any performance details available for the D8 Double Bubble engines?
For the D8 Double Bubble, what are the thrust requirements for the engines? Has it been stated what the estimated max thrust will be for each engine?

Source: sputniknews.com

All details in: NASA N+3 MIT Team Final Review. for the D8.5: 3 geared turbofans, boundary layer ingestion, bypass ratio of 20 and 37.7 kN.

@mins 37.7 kN sounds like the answer... ;)

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Do planes turn while climbing? Is this because of air characteristics variation?
I've developed the impression that often commercial planes will bank and turn as they climb across thin cloud layers that appears to be stratus or stratocumulus.
I think these clouds indicate a separation between different air masses. So my question is two-fold:

Are planes actually doing this or is it a coincidence?
If not a coincidence, what is the reason? and what would happen if they didn't?

Welcome to Aviation SE.
There is no need or reason to turn when going through clouds.  Aircraft frequently climb (or descend) and change direction at the same time.  If it happens in cloud, it's just a co-incidence.
As an example, on an approach, ATC often issue instructions such as:

Turn left heading 300 degrees, descend and maintain 4000 feet.

The pilot will start turning towards heading 300 and start descending at the same time.

Resume own navigation, climb flight level 370.

Following a previous instruction to deviate from the heading on the flight plan, the pilot is now cleared to turn back onto the planned track and climb to the planned flight level.
There is a high probability that you will see aircraft turning in clouds since arrival and departure routes, which is when most of the turning, climbing and descending is done, are when you are most likely to see aircraft in and out of clouds and manoeuvring.
In cruise, when an aircraft turns, it is also common to descend or climb since the altitude flown according to the heading is determined by the quadrantal and hemispheric rules.

You're most likely to go through a cloud layer when you're climbing or descending. You're quite likely to climb or descend when you turn because it is common to separate traffic going in different directions into different altitudes to make separation simpler and more effective.

@DavidSchwartz Good point.  Mind if I edit it in?  Or perhaps you could add this as another answer since it's entirely relevant to the question.

Feel free to edit it in. Then I'll delete my comment if it's not longer relevant (and/or this one depending on how you edit).

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
How are Max Brake Energy Speed & Weight affected by other factors?
I'm a student pilot and I'm trying to understand how different factors affect VMBE and Maximum Brake Energy Limited Take-off Mass. I made some researches but I couldn't find anywhere a clear answer.
What is the effect of Density, Flaps, Mass, Runway Slope, Runway Contamination ?
I know that to solve these kind of problems we use the kinetic energy formula: $\small Eb = \frac 1 2 MV^2$ but I don't know how to use it to explain the effect of every factor mentioned above.
(I need your help because I don't want to just learn things by heart and not be able to explain that in an interview or whatever).

The factors you mention will affect how much energy the aircraft has that's going to be transferred into the brakes, and how much will be lost otherwise.  The more energy you have, the slower you can go before the brakes are overwhelmed -- thus, reducing your VMBE.
With more flaps, energy will be dissipated in aerodynamic drag, although probably not all that much (though going from the least possible to the greatest possible flaps may make some difference -- or it may be sufficiently slight that the charts are published with a worst-case scenario & if you have greater flaps then your situation will be slightly better than what's charted).  With runway gradient, you'll dissipate some energy rolling uphill, while you'll have more energy (potential energy becomes kinetic energy) rolling downhill.
The really significant factor is aircraft weight, as your formula makes clear... an aircraft stopping at 100,000# will have 2/3 of the energy of an aircraft stopping at 150,000#, all else being equal.  So, in those two cases VMBE would be much higher for the 100k case... if Limit = 0.5 * wt * V-squared, you can have a higher V-squared to reach the same limit with a lower weight.
Contamination probably wouldn't matter much: while you would be transferring energy more slowly into the brakes stopping on a slick runway than on a dry one, the total energy absorbed into the brakes would be the same.  So unless the rate that the energy is absorbed changes the maximum energy that the brakes can absorb (seems like it would be unlikely, although in some cases... who knows), contamination wouldn't affect VMBE.  (Unless the charts take stopping credit for the deceleration due to "plowing through" contamination -- which would actually help out to some extent.
The most likely effect would be to make the stopping distance more limiting in the contaminated case than it would be otherwise -- so you might be limited by the ability to stop before the end of the runway in a contaminated case, where you'd be limited by brake energy in a dry runway case.
The effect of weight, flaps, and slope on the actual VMBE would be that things which give the aircraft more energy (more weight, less flaps, downhill slope) would reduce the VMBE.  Think of it in an extreme case... if you had the brakes of a bicycle, a one-pound vehicle could go insanely fast before you could put enough energy into the brakes to cause a problem, but if your vehicle were, say, the Space Shuttle, even at slight speed, the brakes would be overwhelmed by the KE of that much mass.  Consider likewise, a 45 degree downslope vs a 45 degree upslope, or the drag caused by a huge drag chute vs the drag of a pencil flying through the air.

Maybe it's clearer to say that VMBE is the maximum speed to reject the take-off within the energy capacity of the brakes alone (Max brake energy speed). Brakes convert kinetic energy into heat. Once the limit is reached, the brakes fade. So above VMBE the brakes will not work.
VMBE is most limited by:

Heavy Mass
Downhill Slopes
High Temperatures (Low Density)
High Pressure Altitudes (Low Density)

On the other hand, if the Allowed T/O Mass is Brake Energy Limited, we need to decrease the Mass (weight) to be able to stop without fading the brakes.
However, runway up-slope will actually help the aeroplane to stop, therefore the brakes will not have to absorb so much energy and the allowed mass will be higher. With a runway down-slope it is the opposite A down-slope will degrade the stopping capability of the aeroplane and therefore the brakes will have to absorb higher energy => brake energy limiting take-off mass will be decreased.
I think in fact that The Brake Energy Limited T/O Mass is mostly dependent on the Decision Speed (V1).

"A maximum V1 speed, limited by brake energy (VMBE), exists for each TOW, this is why it seems to grow more limiting as V1 increases. To achieve a higher V1 speed, it is necessary to reduce TOW"
Correct me if I'm wrong.

Your V1 can't be greater than your rotation speed, nor can it be greater than your accelerate-stop speed, which may be limited by runway available, or by VMBE. On a long runway, VMBE might be more limiting; on a short runway, the ability to simply stop the aircraft will be more limiting. Both of these limits are more restrictive at heavy weights than at light weights, while V1 limited by rotation speed goes up with increasing weight. Whichever limit is most restrictive, applies.

I totally agree, many factors are linked in some way, I'm asking these questions in order to be able to solve questions in the ATPL and interview in the future, in order to do so i think I need to take each factor separately but indeed in real life everything plays a role! Thank you for you answer it's helpful anyways ;)


text:
How good is the ground visibility by a moonless night In the Grand Canyon?
My night flying experience is limited to light-polluted coastal southern California.
When flying over low-population countryside on a clear, moonless night, do the stars provide enough light to identify the contour of the ground or is it completely dark?
If anyone has specific knowledge of flying over the Grand Canyon at lowish altitude under those conditions, I would appreciate your impressions.
Background - I'm writing a fiction novel where characters make that flight and want to accurately describe what they can see if anything.

Note that flying close to terrain in the grand canyon is subject to restrictions: https://aviation.stackexchange.com/questions/8135/can-i-fly-into-the-grand-canyon

@CodyP Thanks for that reference. This story's sci-fi and it's a military flight during a state of emergency.

No, in a remote area on a moonless night, it’s a black hole.  It’s the blackest darkness you can imagine with a few pinpricks of light from remote settlements on the ground or vehicles.  I have heard a few stories from pilots flying at higher altitudes on moonless nights, such as Maj Brian Shul who did this over the Arctic Ocean in an SR-71, where they shut down cockpit lighting and found that starlight was intense enough to illuminate their instruments.  I also know of tales from Navy pilots who have flown fighters in dark night over water who can’t see anything out in front of them.
These conditions require total reliance on instruments to know which way is up and plenty of people have become spatially disoriented flying like this and crashed.  I have heard some hairraising tales from drug runners like Barry Seal, Carlos Lehder, etc., who used to fly airplanes low level over the ocean at night in order to avoid detection, remaining about 50ft or so off the deck.  One guy they interviewed for the MSNBC documentary Cocaine Cowboys used to do this approaching the Keyes south of Miami for a drop off.  He used to say if he could see the light glow of Miami off his nose he was fine but if he could see the glow from both Miami and Tampa, he was too high and risked detection.  God help you if you had a bad altimeter setting in these conditions.
I will make my own comment, as a professional pilot, that dark night conditions over remote areas or open water are downright eerie and there’s is always an uncomfortable feeling in myself when doing PIC operations in these condition.

Then there’s the story Jim Lovell told about following a trail of bioluminescent algae to his aircraft carrier. Gotta be pretty dang dark to see that!

@TomMcW: I recall the story. Was it retold in the movie Apollo 13?

@EricJ. Yeah. He talked about it during an interview and Tom Hanks repeated the story in the film.

Having had the pleasure of seeing what bioluminescent algea look like recently, I would say it's entirely possible; they're surprisingly bright.

I did a SCUBA night dive in those conditions. When you move your fingers through the water, in pitch darkness 40' underwater, it looks like faerie fire coming from your fingertips.

I presume the drug runners were using aircraft not equipped with radar altimeters?


text:
What is the reason to have LOC/VNAV landing method?
What is purpose of mixing LOC/VNAV in this landing method?

The purpose is landing, could you be a bit more specific with your question?

There are many landing modes (FLS, ILS, MLS etc..)  but when will we use Mix LOC/VNAV landing method ?

A VNAV with localiser approach is normally a backup to a regular ILS should there be a glide slope unserviceability. The use of VNAV  to manage the vertical portion of the approach would allow the use of APV minima which are normally lower than using a vertical speed mode.
VNAV is a better mode when conducting non-precision approaches as the aircraft is still following a defined glideslope - albeit derived from a database - which is more accurate than trying to follow a tabled set of heights and distances using vertical speed.


text:
What are the advantages and disadvantages of elevons?
I'm in as student, I wanted to know the advantages and disadvantages of elevons?

Image source
The advantage is: if there is limited real estate available for flight control surfaces, you don't have to divide it up into elevators and ailerons and only use half the available surface for pitch or roll.
The disadvantage is: you cannot go past the surface stop, and there will be situations where a combined pitch and roll cannot be commanded fully by the elevons because one of the surfaces will run into its stop. Resulting in smaller roll & pitch responses than commanded, in only certain situations.


text:
Do you say prefix K for airport codes in the US when talking with ATC?
I'm a new student, and I see the US airport codes on charts with the K prefix, e.g. KORD for Chicago O'Hare.
I have always seen on commercial flight booking sites, only the last three, letters such as "ORD" are displayed.
Are pilots meant to pronounce the full code or just the letters after the prefix, assuming the K prefix, when talking with ATC?

Note the US, Canada, Australia and a number of islands are exceptions to the ICAO code prefix system. In other countries the ICAO code doesn't really match the IATA code (which is only used for commercial matters). The former begins by a "continent" code (e.g. L for Southern Europe), a country code (e.g. F for France) and ends with a local airport code. CDG is the IATA code for Paris Charles De Gaulle, but the ICAO code is LFPG (P for Paris FIR), similarly Paris Orly is coded ORY and LFPO.

@mins In the U.S., there's a separate system. Not all U.S. aerodromes have an ICAO identifier, but all of them have an FAA identifier, which is typically 3 letters for larger public use airfields, 3 alphanumeric characters for smaller public use airfields, and 4 alphanumeric characters for private ones. While ORD is indeed the IATA code for O'Hare, it's also the official FAA identifier for O'Hare. For U.S. airports that have an IATA code, it usually matches the FAA identifier. For U.S. airports that have an ICAO identifier, it's usually the FAA identifier with a 'K' or 'P' prepended.

@reirab: Interesting, so for ATC purposes we use the ICAO code, and never the IATA code. In the US, FAA playing the role of ATC regulator has assigned FAA codes to be used in place of ICAO codes. They happen to be the same than IATA codes when there is one. In addition prefixing FAA code with K/P gives the ICAO code...?

@mins Yeah, that's basically how it (usually) works. K is the continental U.S. while P is Northern Pacific region (e.g. Hawaii, Alaska, Guam, Saipan, etc.) I'd assume that the primary reason for the separate system is the enormous number of aerodromes in the U.S. They peaked at a bit over 20,000 in 2007, while K + 3 letters only gives 17,576 possible combinations. This graphic kind of puts it in perspective, though it doesn't appear to include helipads or seaplane ports.

As a private pilot, I can't offhand recall ever having used those airport codes, or hearing them used, when talking to ATC.

@jamesqf I have used the codes in ATC comms, either of my own volition or by request, typically to clarify which airport I am asking for clearance to, or similar.

There are actually two separate coding systems in play here.
IATA (International Air Transport Association) codes are 3 letters and are used for commercial bookings etc. They are assigned only to commercial airports throughout the world. ORD is the IATA code for Chicago O'Hare.
Pilots and ATC use the four letter ICAO (International Civil Aviation Authority) codes, which are assigned to every public-accessible airfield in the world. These are systematically allocated with the first one or two letters indicating the country. K is used as the first letter of airfields in the continental US (with separate codes for Alaska, Hawaii & territories in the Pacific/Caribbean matching regional standards).
Commercial airports in the continental US tend to have the two codes in matching pairs such as ORD/KORD, LAX/KLAX etc but this is not the case in other countries. Manchester, UK has IATA code MAN but ICAO code EGCC.
Meanwhile smaller airfields in the US may only have an ICAO code, where the corresponding IATA code (minus the K) could belong to an international airport elsewhere in the world (for instance KPRG is Edgar County Airport, Illinois and PRG is Prague Václav Havel Airport, Czech Rep.).
Finally, the very smallest airfields in the US (typically private/restricted access fields, in any case not large enough to warrant an ICAO code) are given a 3- or 4-character code by the FAA which extends the ICAO system by allowing digits as well as letters. Small public fields have a 3 character code (eg 9S2 or C97) while private fields have 4 characters which typically include the state abbreviation eg TX05.
For more details of the exact determination of which code type a US airfield is assigned by the FAA, see reirab's excellent self-answered question: How does the FAA determine which format of location identifier to assign to an airport?

Actually, the K prefix only applies to the continental US.  Alaska and Hawaii are part of the Pacific region code.  Alaska airports start with PA. Anchorage (IATA ANC) is PANC. Hawaii airports start with PH. Honolulu (IATA HNL) is PHNL.

Good point, will edit

IATA is the International Air Transport Association. It's an airline industry trade group. Also, all U.S. registered aerodromes have an FAA identifier. ICAO ones are mostly only assigned to airports that have scheduled passenger service and/or a non-trivial amount of international traffic.

@reirab thanks for the correction, i should have looked it up instead of relying on memory!

I don’t know if it is a correlation or causation, but almost all airfields with a three letter identification (and therefore an ICAO code) have weather reporting capability. Almost no fields with digits in their code have weather.

@JScarry Right, though I would clarify that these small airfields often do have weather reporting (SuperAWOS, etc) but it may not be published and often does not offer ceiling. These are important factors for air carrier operations.

@JScarry Rather than answer in a long comment, I decided to write a self-answered question for this: How does the FAA determine which format of location identifier to assign to an airport?

@reirab I've incorporated a link to your new question in the body of my answer, hope that's OK.

@IanF1 No problem at all. Thanks.

@JScarry weather stations tend to be limited to larger facilities, fields with numeric codes tend to be smaller facilities (private or public). They didn't get the code for their lack of weather station, it's simply coincidence.

@jwenting Weather observation facilities actually are a condition for 3-letter FAA identifiers. AWOS level III + runway of at least 5,000 ft is one of the classes of airports eligible for 3-letter FAA identifiers, though fields given an identifier before their runway was lengthened or before they got an AWOS keep their original identifier unless there's a larger change, such as adding scheduled air carrier service. The criteria for assigning those identifiers is detailed in the question I linked in my earlier comment if you're interested.

Actually there are three systems: ICAO, IATA, and FAA Location ID (you can see this when you look at any US airport on Wikipedia). As you point out, usually the IATA code is the ICAO code without the K, and usually the FAA LID is exactly the IATA code, but not always. When talking to US ATC, what we want is the FAA LID.

How are private fields coded with FAA LIDs if there are more than 100 in the state?

@Someone they can re-arrange where the numbers are placed in relation to the letters. For example TX00, 0TX0, and 00TX would be valid and unique LIDs for private airports in Texas. And if they run out of identifiers which use the USPS two-letter abbreviation for the state they can get creative. For example, just panning around east of IAH I see 1XS1, TA07, 3TE1, etc...

The other answers have lots of excellent context & background info, but to give the direct answer to the direct question, *no, you don't use the "K" * with ATC under normal circumstances.
The (rare) exception will be when it is necessary for some reason, but that is almost never. In voice communication, "direct Midland VOR" or "direct Midland airport" are used, rather than "direct MAF" or "direct KMAF".  Obviously, printed NOTAMS and flight planning work differently.
If you were to be cleared "direct MAF" (which is both the 3-letter FAA ID for Midland, and also the non-colocated VOR), it would be appropriate to query "is that the airport or the VOR?" if you aren't sure. (If you are navigating VOR to VOR to MAF & beyond, you could safely assume the VOR; if your destination is Midland, asking the controller would be appropriate.)
But when asking you to "say destination," it's understood you're landing at the airport rather than the navaid out in the field!

Well, shouldn't you extend it to "no, you don't use the "K", but you don't use the other three letters either"? Because that's the point—you use the name, not the identifier.

The name is most common, but there can be times when you're asked to "say destination", and if it's far enough away that the controller isn't familiar with the name, then you would give the 3-character FAA ID -- be it MAF or 9S2 or whatever.  But KMAF would be unnecessary and it isn't the way I hear it on ATC.

As an FAA controller in the Terminal specialty (i.e. not an ARTCC controller) in the Lower 48:
NO.
No no no.
No no no no no no no no no.
NOOOOOOOOOOOOOOOOOOOOOOOOOO
You're a pilot in the USA. We're controllers in the USA. We don't need the Kilo. We don't want the Kilo. The Kilo is extraneous information that no one cares about when you're talking on the radio.
But more annoyingly than that, when you call asking for flight following we have to enter your destination using the FAA's three-letter code, no Kilo. If we enter four characters the system doesn't accept it. No bueno. Error. You will not go to space today.
So we're typing along, quick-quick-quick, trying to remember your type code (because in another annoyance, we have to enter your tail number, then your destination, then your type code, then your altitude, in that order and no other)—and you say you want flight following to KILO-PAPA-DELTA-XRAY and we type the K and then we have to backspace and type it out again and now it's a bad day.
So don't use it.
Please and thank you.

The "K prefixed" and the "non-K prefixed" codes are actually different designation systems. The former is used by ICAO and the latter by IATA, and each have specific use cases by different authorities.
Not all airports in the world have their ICAO and IATA codes differentiated by leading K (an airport might not even have both). This is usually holds true only to the larger airports and only in the US. In case of airports in the rest of the world this is not true: some airports' ICAO and IATA codes are totally different from each other, while others' do bear some varying degree of similarity.
You can get an idea by looking at these lists: https://en.wikipedia.org/wiki/List_of_airports_by_IATA_and_ICAO_code
http://www.flugzeuginfo.net/table_airportcodes_country-location_en.php

"Not all airports in the world have their ICAO and IATA codes differentiated by leading K" In particular, all the ones outside the US, since the K- prefix denotes an airport in the continental USA.

@DavidRicherby Indeed. "This is usually holds true only to the larger airports and only in the US"

But it doesnt "usually hold true". It's completely specific to the USA. It's like saying "Not all countries in the world have a capital called Washington."

@DavidRicherby I think the 'usually' is regarding whether airports elsewhere are "some other letter + IATA code", which is true for some airports outside the continental US - mostly in Canada, and the "P"acific airports in the US as mentioned in another answer, and a handful of others worldwide.

IATA codes are not used when communicating with ATC.  In cases where the FAA identifier matches the IATA code (nearly all major US commercial airports), the difference is transparent, but when things don't match up, IATA is used at the ticket counter but not on the radio.

When programming your GPS or FMS you need to distinguish between airports and VORs e.g. KLAX is an airport and LAX is a VOR on the airport. But controllers rarely say the letters and instead use the names for airports and VORs. It is usually clear from the context and the destination that the pilot has filed.
A typical clearance from my airport might be Crepe Three departure, Morro Bay transition, San Marcus then as filed. The pilot knows to follow the CREPE3 departure which terminates at MQO and then direct to FLW and from there whatever was filed.
When asking for VFR flight following, pilots usually just give the name of the destination airport unless there are multiple airports in the same city. For example, Bakersfield has two airports so to make sure the controller knows where you want to go you would give the identifier, either BFL or L45. Also, if you are going to a small airport outside of the local area the controller may not have heard of it and will ask for the identifier.
I don’t recall hearing anyone say the identifier with a K when talking on the radio. But that’s not necessarily something I’d notice. You might want to listen to some of the clearance delivery channels on LiveATC to get a feel for how pilots and ATC communicate routes.

Usually, yes, and in particular when using the airport for position reporting.  Sometimes there will be a VOR or VORTAC which uses the same three letter identifier nearby or collocated on the airport so it can cause confusion for a controller.

In my experience, you usually use the NAME of the airport (or navaid).  Center controllers are well familiar with their AOR (and usually adjacent ones just by experience).
Now for longer VFR flights where you may be crossing multiple centers, they may not recognize the named airport, so giving them the identifier can be helpful.  This is not an issue for IFR where they already have your full plan.
Finally, a 'little secret' is that the name an airport is called locally is often different than the name in your AFD. For example, Lewis A Jackson Regional Airport (I19) in Xenia Ohio is "Greene County" (not "Jackson Regional").  Calling the FBO on the phone before flight will uncover that, or listening on the radio as you approach.  If unsure, go ahead and append the identifier to the name you guess it should be called.  Yeah, you're chewing bandwidth, but that's more efficient than the back and forth and better than a mistaken ID.


text:
Aerofoil Lift curve
so I’m trying to identify if my aerofoil of choice, 24xx can generate enough lift.
I’ve been trying to find a Clmax against angle of attack curve online but I can’t seem to find one? Anyone know any good websites for this sort of thing?
Also, any recommendations please on what criteria i should be looking for other than t/c and Mach number when selecting my aerofoil please?
CLmax:1.60
Max mach: 0.29

A quick Google search for "naca 2412 lift" gave this: http://airfoiltools.com/airfoil/details?airfoil=naca2412-il
They have these curves for probably any NACA airfoil and a ton others - so just type the airfoil name in that little search box at the top ! ;)

Hi thanks mate! I was trying Java foil but was a little more complicated


text:
Calendar months "preceding month" vs "before date"?
What is the difference between 14 CFR 61.39(a)(6)(i) which states, "Has received and logged training time within 2 calendar months preceding the month of the application in preparation for the practical test", and 61.65(d)(2)(i) which states, "Three hours of instrument flight training from an authorized instructor in an airplane that is appropriate to the instrument-airplane rating within 2 calendar months before the date of the practical test"?

Namely, what is the difference between the language "preceding the month of" and "before the date of"? Is there any difference? (If not, why not use the same language?) It seems like 2 calendar months before the date of, say, March 15 could mean January 15. That would have a different meaning than 2 calendar months before March itself, which could mean anytime in January.

This is using a possible specific definition from Webster's for Calendar Months:

Definition of calendar month
1: one of the months as named in the calendar
2: the period from a day of one month to the corresponding day of the next month if such exists or if not to the last day of the next month (as from January 3 to February 3 or from January 31 to February 29)"

I realize I'm probably over thinking this, and guessing they mean the same thing, but it would be nice to know for sure. Asking because there have been reports at my school of a student that failed their oral exam because they didn't know the correct definition of "calendar month", and how it applies.

Apologies about any faux pas in this post, it's my first time!

References:
https://www.law.cornell.edu/cfr/text/14/61.39
https://www.law.cornell.edu/cfr/text/14/61.65
https://www.merriam-webster.com/dictionary/calendar%20month

The way I read these two statements.

61.39(a)(6)(i) - Has received and logged training time within 2 calendar months preceding the month of application in preparation for the practical test;

This statement means that you can take the practical test on April 30th but must have received training after February 1st.  This could be 88 days between the last training flight and the practical test.

61.65(d)(2)(i) - Three hours of instrument flight training from an authorized instructor in an airplane that is appropriate to the instrument-airplane rating within 2 calendar months before the date of the practical test; and

This statement means you can take the practical the practical test on April 30th but must have received training after February 28th.  This could be 61 days between the last training flight and the practical test.

I think you're right, but man is that confusing.  They could have just said "60 days" and achieved the same objective without the confusion.

Yes! While it seems likely they should have the same meaning, it's also very easy to read them as being different!

@757toga.  61.39 is the requirement for any practical test and 61.65 is more restrictive for an instrument rating.

good discussion of this question and analysis on reddit's /r/flying.


text:
Why aren't all fighter jets' engine intakes on top instead of forward?
Reading the question and answer to How does the Yak-130 fly with blocked engine inlets, I am now wondering why it - or any fighter jet - has forward engine intakes at all? The top and accepted answer indicates the forward engine inlets are closed when taking off from unprepared fields to avoid foreign object damage (FOD) to the engines, and inlets on the top are opened at the same time.
If the inlets on the top can supply enough air for the engine during takeoff - the phase of flight with the most demands on the engine - why not use them all the time and simply not have forward inlets at all? It would simplify the design, protect the engines from FOD all the time, and probably offer a few other benefits, but I'm sure there's a big trade-off - maybe stealth? Fuel consumption?

Already we have good answers, so just a tl;dr comment:  FOD doesn't matter for most of the mission, so optimize airflow for the common case.

HEH, I was going to ask the same thing after reading the same referenced question :)

Interest only: B2 does not use taxiways, to limit FOD. They reverse taxi on the main runway and then turn round. (AFAIK)

When the inlets are on top, the air entering the engine must make a 90 degree turn to get into the engine.  This will cause inefficiencies and might cause massive separation -- which would be very bad.
At high thrust and low speed, the flow can stay attached and the engine can tolerate inefficiency (takeoff and landing are a short period of the overall mission).
At high speed cruise conditions (for a subsonic aircraft), you need to use the flow decelerating into the straight-in ducts -- and you can't suffer the losses that would accompany a 90 degree turn.
If you're supersonic, it gets even worse -- fighter jet inlets are mostly designed around supersonic operation, with lots of doors, ramps and other contraptions to make them operate at other conditions.  The faster the cruise, the more complex the inlets.

Adding onto this great answer: as far as I understand them, you dont want supersonic airflow (specifically the shock front) entering the compressor stage of a gas generator (the 'jet engine'). Even the ramjet mode of the J58s (SR-71 engines) slows incoming airflow to subsonic utilizing the ram effect to feed air past most of the compressor stages and into the burner. However, keep in mind, air going into the big forward intakes is still used for thrust, so even if its slowed down it is adding pressure, thus gaining some 'ram air' efficiency gains even to non-ram designs.

Even subsonic aircraft use their inlets to slow down air.  A transport aircraft at Mach 0.85 has a fan front face Mach number of about 0.6.

Forward-facing intakes provide ram air compression, which convert airspeed into additional pressure. This significantly improves engine performance if there's any significant airspeed.
It's true that takeoff is the most demanding phase in terms of static thrust. However, it's not always the most demanding overall. At altitude, air is less dense, so more air is needed by volume. Ram air effect helps collect and compress it.
The opposite happens to a side- or top-facing intake: air has to be accelerated with low pressure to "suck it in", reducing both efficiency and mass air flow, and thus thrust. A fighter with top-only intakes would underperform at high altitude, like a piston plane without a turbo- or supercharger. High-g turns would also be an issue.
Some Russian jets are built with rough field features like top air intakes after the lessons of Barbarossa, when Germany bombed most of their frontline airfields with a first strike, leaving many aircraft on the ground, flyable, but unable to take off due to runway damage. That's a useful feature in wartime, but even these jets switch to forward-facing intakes once they clear the runway.

It's true that takeoff is the most demanding phase in terms of static thrust. - Is that really true for a fighter?  Their thrust-to-weight ratios are usually pretty high so getting off the ground isn't a big deal unless there's a limited runway length (or rough surfaces like you mention later).  But intercepting other aircraft also has high thrust requirements, for rate of climb and for speed, plus dogfights to maintain airspeed in high-G turns.  Unlike a transport plane, it matters what happens after getting off the ground.  (I realize this is just a nitpick over phrasing.)

@PeterCordes Yes, even for a fighter, takeoff requires the most static thrust. On some USAF bases, and needless to say in the USN, full afterburners are used for takeoff. Full afterburner at sea level is the most thrust the engines can produce. High-speed interception is the second-highest-thrust scenario.

@Therac I think the confusion is that it's not necessarily true that takeoff is the most demanding, it just happens to be true in essentially all cases. For an extreme example, the Bell X-1 had a very easy takeoff regime separate from the B-52, already at speed), and much higher thrust required later. There are doubtless other edge cases, but you are still correct in general that takeoff is most demanding.

Takeoff is only a small part of the flight regime. And not necessarily the most demanding.
A high G turn , where the inlet on the top of the wingroot is in the shadow of the airflow...air intake is diminished, right when the engines need it the most.
The vast majority of fighter aircraft do not need such FOD protection in daily use. British, French, German, US, Swedish. Not everyone has FOD filled runways.
Or can't spare a few maintenance people to do a FOD walk before daily ops.

"Lack of runway FOD walker personnel"  is not why Russia builds FOD resistance into their jets. NATO aircraft require first-rate facillities,  and Russia has those too but expect them all to be smashed in the first hour of a war. NATO spends a fortune protecting those bases and on ability to fight from distant bases (e.g. midair refueling) and Russia says, "we'll just base in a random farmer's barn and use his farm road as a runway, hence, rough field gear and good FOD protection".  This doctrine saved Ukraine's air force, and may show the dainty F-16 to be a misfit in Ukraine.


text:
Ground Handoff to Tower
When a plane is passed from the ground to the tower, do the ground controllers have to give the tower frequency? For example, "N123B Contact Tower on 121.32" rather than "N123B Contact Tower"

At the towered airports I fly out of, typically class D and C here in the US there is no explicit handoff to tower but rather you call the tower when you get to the hold short line. The sequence from the ramp goes:

N123AB: Ground, N123AB at the ramp with the weather requesting taxi to the active runway

Ground: N123AB taxi to Runway 26 via romeo alpha

N123AB: Taxi runway 26 via romeo alpha

Then when your at the hold short line you tune your radio to tower

N123AB: Tower, N123AB is holding short Runway 26 at alpha

Tower: N123AB cleared for takeoff runway 26

"the weather" is identified by an alphabetic designator that rotates so for example might be "with echo"
There is typically one tower frequency which is why a frequency is often not given but at large airports like KJFK which has multiple tower frequencies depending on the runway you are taxing to
Small class D airports, during non busy times, may have the tower controller also working ground but a frequency change is still required on departure. In my experience on landing the tower will sometimes issue "taxi to the ramp via romeo alpha with me" indicating not to call ground to get your taxi instructions.

This question is also related


text:
Role of Spoilers in Conjunction with Flaps A350
Upon observing the Airbus A350, I have noticed that both the outboard and a few of the inboard spoilers are deployed maybe three quarters of an inch when the flaps are fully extended. I assume this is to aid in drag reduction, as evidenced by numerous videos I have watched.

Does this answer your question? Why do outboard spoilers deploy more than the inboard spoiler on the A320?

Why would opening spoilers reduce drag?

@sophit -- I don't see this as a duplicate.  Questioner is implying that spoilers are always slightly open whenever flaps are fully deployed-- I don't see how the other question addresses why that would be the case (if it in fact is).

@quietflyer: well that answer explains why Airbus uses flaps in conjunction with spoilers, which is also what has been asked in the present question, so for me if not a complete duplicate it is anyway very similar.

@quietflyer Well as the outboard spoiler is slightly down it has slightly less parasitical drag, as it's not 'fully up'

@sophit If it is not a complete duplicate, then please don't vote to close as a duplicate. The answer to the other question does not nicely answer this question. Half a year ago, we discussed the lack of opportunities for new users like yourself to contribute to the site because so many interesting questions were closed as duplicate, even if they were not. Here is an opportunity to explain about wing design and movable surfaces, slotted flaps, boundary layer separation and laminar flow over the flap, and you want to close it? Quick, write a stellar answer before somebody else does!

@DeltaLima: I'd let the questioner decide if that answers its question  If not, I'd be glad to elaborate an answer.

The other thread doesn't accurately answer my question as the spoilers on the A350 are all the way "in" as compared to an Airbus when they're fully extended...

I just found something that said the deployment of the flaps on bigger aircraft are to help with stability primarily on the rolling axis at lower speeds... Wen the flaps ar extended the ailerons become less effective, as the increased camber of the wing causes the ailerons to be less useful in the airflow.


text:
Why does the hardpoint mechanism on sweep wings produce a contact trace in front of the axis?
The basic structure and photos have already been explained on this site and on Wikipedia:

How does a variable-sweep-wing aircraft keep wing-mounted payloads straight?

Variable-sweep wing, Wikipedia

Looking at it, I understood that the pin and pivot that make up the axis of rotation and the link bar provided in front of that axis form the basic mechanical structure.
However, it is not clear why the structure produces traces of contact only in front of the axis on the undersurface skin of the wing.

Modified from an answer here

My guess is that it is equipped with a guide contact. However, such a policy stresses thin skins. I also speculate that the skin is not an accurate plane. That seems absurd.
I also considered the deformation of the pylon as a candidate, but from the viewpoint of the aerodynamics of the payload, I thought that the upward aerodynamics would not be applied to the front because it moves downward from the head when falling.
Please tell me why the structure has an arc mark in front.

maybe it produces an arc on the trailing edge too, but you can't see it in these images because of the angle. 2) The skin is thin, but maybe it's reinforced in these areas to accept the stress of the contact/motion. Also, use @ to address a user by name, it will actually send them a notification.

Are you sure that’s not a painted arc to show the sweep limits of the pylon?

Maybe making the geometry close-fitting enough that the pylon rubs in front as it rotates, creates a more rigid structure?

“My guess is that it is equipped with a guide contact. However, such a policy stresses thin skins.”—it's OK to stress the skin where you know about it and can strengthen it appropriately. In fact it's better than random stress somewhere you don't expect it as would happen if it wasn't supposed to touch, but occasionally did as it flexes in flight.

Having put on probably hundreds of pivot pylons on an F-111E back in the late '70's, the pylon is NOT attached to the skin.
There is one large attachment collar. Teeth on the pylon meshes with teeth on the wing hardpoint, to manage the rotation.
All the wiring for the pylon and weapons features feed through that hollow collar. It is actually a real PITA to install these. IIRC there are 7-9 cables that feed through here, some of them reasonably large.

https://www.researchgate.net/figure/Diagram-of-F-111-Pivot-Pylon-Assembly_fig8_38134670
The F-111 has 4 hardpoints on each wing, but only the inner two on each wing pivot.
To address the original question:
Just a supposition on my part for the Tornado and that black stripe, but I would surmise that is is an extra paint layer, to wear away as the pylon pivots back and forth, being rubbed by the flex material at the front. An indicator of how much paint has worn away...once you see grey, repaint the black arc.
To address a comment...
If there is contact between the wing skin/paint and the flex material at the front of the pylon, the pain is going to get rubbed off over time as the pylon rotates back and forth. Again, supposition because I never worked on the Tornado, but maybe a rough wear indicator.

This does not actually answer the question?

"being rubbed by the flex material at the front."-- can you expand your answer to say a little bit more about this?  What is the "flex material"?

Thank you for your wonderful answers.
I understand that the fact that the operating range is marked is also the case in the photo. I also found that the application of a structure that allows contact is sufficient for the skin to withstand. I also understood that it could actually be scratched for some reason. I've never heard of the existence of a stretchable sleeve. Providing many detailed photos was very helpful to me. Thank you everyone.


text:
Is there a regulatory maximum side slip angle for commercial aircraft?
Hi am currently trying to run Dutch roll simulations for a proposed 35 seat twin engine turboprop aircraft.
I was just trying to work out what sideslip angle might be appropriate to use. Is there a maximum side slip angle for commercial aircrafts, if so I would like to use it to access the aircrafts performance at that angle. I heard something about 15 degrees.

Dutch Roll might not involve huge sideslip angles - some of course - are you talking about maximum slip angle that a/c systems permit?  Or that a/c can tolerate w/o breaking?  Is yaw damper on?  What is pilot doing with rudder pedals?  Etc- need more info.  Or are you asking about a regulation?

@quietflyer yes more talking about regulation

There is no regulatory maximum for side-slip angle. There are requirements that there be sufficient lateral control in an engine out condition.

§ 25.147 Directional and lateral control.
(a) Directional control; general.  It must be possible, with the wings
level, to yaw into the operative engine and to safely make a
reasonably sudden change in heading of up to 15 degrees in the
direction of the critical inoperative engine. This must be shown at
1.3 VSR1 for heading changes up to 15 degrees (except that the heading change at which the rudder pedal force is 150 pounds need not be
exceeded), and with -
(1) The critical engine inoperative and its propeller in the minimum
drag position;
(2) The power required for level flight at 1.3 VSR1, but not more than
maximum continuous power;
(3) The most unfavorable center of gravity;
(4) Landing gear retracted;
(5) Flaps in the approach position; and
(6) Maximum landing weight.

So a minimum of 15 degrees is expected in the above conditions.
It also goes on to require (I skipped (b) as it addresses 4 engine a/c);

(c) Lateral control; general.  It must be possible to make 20° banked
turns, with and against the inoperative engine, from steady flight at
a speed equal to 1.3 VSR1, with -
(1) The critical engine inoperative and its propeller (if applicable)
in the minimum drag position;
(2) The remaining engines at maximum continuous power;
(3) The most unfavorable center of gravity;
(4) Landing gear
(i) retracted and
(ii) extended;
(5) Flaps in the most favorable climb position; and
(6) Maximum takeoff weight.

Again, with an engine out, the slip angle can be significant.
It's also not unusual to see similar slip angles when de-crabbing during the flare of a crosswind landing.
There are requirements for static lateral-directional stability § 25.177 Static lateral-directional stability. and dynamic stability (including Dutch roll) § 25.181 Dynamic stability..
But all of these are based on the flight characteristics of the aircraft that is being certificated. What you need to model is the aircraft flight characteristics. It will determine what type of Dutch roll behavior the aircraft has. You don't model a Dutch roll and apply it to the aircraft. Different aircraft can have very different Dutch roll modes.


text:
What is a rough estimate for a sideslip angle for a Dutch Roll?
I previously asked: Is there a regulatory maximum side slip angle for commercial aircraft?
Apart from a regulatory maximum, can anyone give me a rough value to assume for sideslip angle during a dutch roll? Is it less than 1?

Does this answer your question? Maximum Side Slip angle for commercial aircraft

I think the question is ok on basic principles (and not a duplicate) but I'm confused about your units.  "1" what?

It seems like you are starting at the end here.  Sideslip angles will be a result of rolling, and will increase, decrease, or stay the same depending on the design, speed, altitude, center of gravity, weight distribution, and (possibly) configuration of the aircraft.
So, starting from your chosen aircraft, it may be best to determine its tendency to Dutch Roll under normal parameters.
Normally, aircraft oscillations stabilize after a few cycles by a process known as "damping".  Imagine a spring attached to a board in your hand.  Bend it once and it will flip back and forth for a while before it stops.
Do this under water and see if you get even one cycle of oscillation.
The drag of the fluid resists motion.
Now take your board out into a hurricane and see what happens.  The oscillations become greater and greater because energy input into the spring is greater than the damping forces.
There are many factors involved with Dutch Rolling, but knowledge of maximum slip angles at what speeds would be very useful, lest someone gets heavy on the rudder at 250 knots and overstresses the vertical stabilizer.

I think the question is fine at least as far as its fundamental philosphy.  Presumably the author means a self-sustaining Dutch roll oscillation that is continuing with no pilot input.  Presumably for any given aircraft at any given airspeed one could specify the max sideslip angle observed in a typical self-sustaining Dutch roll oscillation, if the aircraft is prone to that sort of thing.  Perhaps the results would vary wildly from aircraft to aircraft but-- if so, that observation could be the basis of an answer as well.

In the analysis we might find that a "slip angle" (or a roll angle) might reduce Dutch Roll tendency, as aircraft become more spirally unstable when bank angle increases.  So, I wonder if coordinating the rudder with the roll rather than trying to fight it is better.


text:
Can anyone identify this crashed Swallow biplane?

Can anyone identify the model of this Swallow biplane?  On August 14, 1929, my great grandfather, Humphrey Woods, was fatally injured in the crash of a plane piloted by Thomas Tobiason.  The plane was intentionally put into a tailspin at 3000 feet to get Woods accustomed to the sensation of spinning.  (Woods was seeking to get his commercial pilot license and needed to be able to recover from a tailspin.)  The plane recovered at 300 feet but went into another spin.  The pilot righted it just before it crashed.  It looks like the front part of the plane hit the ground with considerable forward force, suggesting that the pilot was trying to generate lift over the wings.  The front landing gear is destroyed but the tail skid remains.
The August 15, 1929 Kansas City Star reported that it was a Swallow biplane.  I do not think that this is a Swallow made while E. M. Laird was with the company.  I would expect to see four struts leaning in the same basic direction, unless the two inner struts were built into the fuselage.  The tail does not look like the New Swallow photos in which the rudder portion of the vertical stabilizer goes all the way to the top.  The tail of this plane does not have the usual contour of other Swallows, perhaps because of damage from the crash.  The shape of the fuselage is not as streamlined as the Swallow TP or the Swallow J5.  It seems more consistent with the Swallow OX-5 and Swallow N4028, which is my best guess at present.
Thank you for your help.  My Dad asked if it was a Laird Swallow on www.earlyaviators.com/elaird03.htm but never received an answer.

That looks like a survivable crash.  He was probably killed by head injuries from lack of a shoulder harness.

According to the text of the article, while Thomas Tobiason was killed in this crash, Humphrey Woods was only "injured seriously".  Maybe he died later after the article was published?

The report: Aircraft Accidents: Letter from the Acting Secretary of Commerce Transmitting, in Response to Senate Resolution No. 206, Information on Aircraft Accidents which Have Occured Between the Dates of May 20, 1926, and May 16, 1930, of which the Department Has a Record. lists the accident on page 150.
The make and model of the aircraft is listed as "Swallow" and the name and model of engine is shown as "Curtiss OX-5".

What does "Do" stand for in this list?

@towe: it is an abbreviation of ditto, meaning "same as the above". Nowadays it is more common to use one or more quotation marks.

Swallow info on Wikipedia

@TonyK Thank you. Yes, I usually use the - " - style.

@Fred Lawson, thank you!  When I noticed the word "Variants," things started making much more sense!

@DeltaLima, I thanked you in a public comment, but I really cannot thank you enough.

@Steve, you are most welcome! I am glad I could help.

The Swallow has the head protection behind the rear pilots cockpit. Varney airlines had 6 original OX-5 Airmail Swallows and they did not have the 'hump'. Neither did the Swallows prior to 1926. You may find the identical design on the Lincoln/Page LP-2 built from 1927. Varney added the diagonal strut to the outer wings after they replaced the OX-5 engines with the Wright 'Whirlwind' motors by June 1, 1926. A 1927 Laird Swallow was found and rebuilt for the 1976 re-enactment with United Airlines support. That plane is in the Seattle Airport. A 1927 was also found and currently flys at the Oshkosh, WI Pioneer airport.
I am doing research on the only 6 Varney Swallows because I have artifacts from the chief pilot Leon D Cuddeback heirs in Idaho.
Robert P Regan

Correction to the above is a later model Swallow most likely a 1927 with the C-7 motor and not the OX-5. The tail is a Swallow rectangle with curve corners and the stabilizer is proper for all Swallows. Even though Stearman helped design the later swallows up to 1929 before he created his own company. There are plenty of Swallow pics and models and photos.

Swallow msn:540 reg:NC5536
owner:Commercial Airways Corp /MO
Cancelled: 30.8.29
is a possibility, but I am not finding any other info online about it, and the accident was not entered into any of the accident databases, which seem to focus mainly on airliner accidents for that time period.
Several Swallows were struck off the register that month but this is the only one of them that was recorded whose owner was near MO - however the records are very incomplete and there could have been others - or the date it was struck off the records simply not recorded.


text:
How to compute the mass flow rate for a turboprop at cruise given the static sea level value?
I am trying to obtain the mass flow rate of the Allison T56-A-15 used on the C130H at cruising altitude (so as to solve the Joule-Brayton cycle at cruising altitude). I know from "Turboshaft, Turboprop and Propfan: database Handbook" that the mass flow rate is 14.7 kg/s at static sea level (not sure about the meaning of this). In order to compute the mass flow rate at cruising altitude, what should I do? I've tried writing $\dot{m} = \rho A_{in} v_{TAS}$ but in this way I obtain a value of mass flow rate that I consider excessive. Any suggestions?

Mass flow is determined by the thrust.

What you are attempting to calculate is an off-design operating condition based on a known reference point (Sea Level Static performance, which is usually off-take performance).
You cannot simply do this by hand, this requires a model for the engine and knowledge of the off-design characteristics of the engine (map characteristics, e.g. compressor map), furthermore you need the cruise power specification.


text:
What is this old seaplane floating on its wing?
I found this picture today in an old set of drawers that bought at an estate sale over 40 years ago.

Is the out-of-focus nature part of the original photo or your photo of it?  I.e, could it be improved?

Is there anything at all on the rear of the photo?  Studio stamps can help with locations and dates simply by their design.

The only thing on the bank is a stamp with the numbers 438

It looks to me to be a Keystone-Loening K-84 flying boat.  Besides the engine configuration and the N struts on the wings, the best confirming tell tale is the open hatch on the wreck, which matches the one in the second image below.
As an ex bush pilot, I'd make an educated guess as to what happened to it and say it probably was damaged on landing, landing hard, or porpoising, or maybe from hitting a deadhead (semi-submerged log) such that it couldn't be taken off again, was run aground to keep from sinking, the people on board were rescued and the plane just left where it was, this being the days before you could airlift damaged airplanes out of the bush with helicopters.
I would imagine the picture was taken by a salvage crew sent out to recover parts some time later (quite a while later from the looks of it), or maybe just a traveller that happened on to it.

Wow!  Nice find.

That prop's tips are scary-close to the windscreen and presumably the pilot's head.

It's very similar to the Anderson Kingfisher homebuilt.  My favourite bit is the suicide door hatch configuration, necessary to crawl out on the nose I guess.


text:
What are the units for the bearing to center of an airport from radio aids to navigation in chart supplement?

Is the bearing to the center of airport for a radio aid to navigation in the chart supplement, true course, magnetic course, is it based on the VOR's radials, or is it something else?

It's almost certainly magnetic. Page 12 of the Chart Supplement (sample airport information) has this information at the bottom (emphasis mine):

All bearings and radials are magnetic unless otherwise specified. All
mileages are nautical unless otherwise noted.
All times are
Coordinated Universal Time (UTC) except as noted. All elevations are
in feet above/below Mean Sea Level (MSL) unless otherwise noted.
The
horizontal reference datum of this publication is North American Datum
of 1983 (NAD83), which for charting purposes is considered equivalent
to World Geodetic System 1984 (WGS 84).

Because this information is in a kind of footnote at the bottom of the page, I suppose you could say that it's possible it only applies to that specific page. However, the mention of "this publication" strongly suggests that the information applies to everything in the Chart Supplement.
You can also see that it distinguishes bearings from radials, meaning that it's highly unlikely that the word "bearing" is being used to mean "radial" on p.27.

Wouldn't the 180 degree bearing at 4.1 NM be equivalent to the 180 degree radial & the same distance? Since both are referenced to magnetic north, I'm not following how there would be any difference.

@RalphJ Perhaps sometimes, but magnetic north moves around and VOR radials don't, or at least not as often. There's no guarantee that radial 180 is always aligned with 180° magnetic.

@RalphJ 2 VOR's next to each other can have significantly different settings of magnetic north based on variation differences at the time each VOR was commissioned.  So 2 nearby VOR's can differ from each other and at the same time both differ significantly from the nearest isogonic line.


text:
Due to the corrective calculations being ground-based, does the reliability of WAAS degrade with increases in altitude?
Since the WAAS system utilizes stations at known, fixed locations on the ground to make determinations for positional correction, is there a loss in the precision or validity of that correction with an increase in altitude?
If there is, how does it scale?  Is the loss in reliability of the correction linear, exponential, is it simply a negligible degradation, etc?

It would help if you could explain why you think that distance from the ground-based reference point in the vertical direction would affect reliability more than distance from the same reference in the horizontal direction. After all, an airplane is generally a half-dozen miles above the station at most, but could be dozens or even hundreds of miles away laterally. If the latter distance doesn't affect reliability, why would the former? Are you really asking strictly about altitude, or about distance generally?

The answer to that question is:  because horizontal distance changes (on the surface)  would tend to affect the straight line distance from a satellite less than moving upward but less as a satellite's orbit approaches the visible horizon from a given point on the surface.

Yes, but it is a fairly small error.
Some of the major sources of GPS error are able to be "corrected" by WAAS.  The WAAS stations are used to build a model to make these corrections.  These corrections are most accurate near each station, and less so the further away from each station.
A couple of the largest errors are due to Satellite clock error and ionosphere delay.  Satellite clock error is "correctable" by WAAS and will only depend on the specific satellite so would not change with receiver location.  (ie when using Satellite number 1, add 1 microsecond...).  On the other hand the ionospheric delay is somewhat location specific (when receiving satellite number 1, while standing at position X, the atmosphere is delaying the signal by Y microseconds). For locations that are not at one of the WAAS ground stations an approximation for the the ionosphere delay must be used.
However, being at altitude is probably not going to change the error by much.  I don't have data on how it scales.

A microsecond is 300 metres (~1000 ft), an insanely huge error for GPS. Normal error is in tens of nanoseconds at worst.

This was meant simply as an example to explain the concept.  An actual correction of 1 microsecond to GPS satellite number 1 should not be used for any air navigation.


text:
Why does the FAA require special authorization to act as PIC in the North American T-28 Trojan?
This airplane doesn't have a max gross takeoff weight of more than 12,500 pounds nor does it have a turbine engine.

The FAA requires special authorization to act as PIC in order to fly it.  What is the reason?

As the T-28 is a vintage military surplus aircraft it is normally certificated in the Experimental-Exhibition category. For most aircraft in this category, there is no type rating in the traditional sense. For years, the FAA managed these aircraft and pilot qualifications for them on a case-by-case basis. Approval to fly them was (and for some vintage aircraft still is) granted by a Letter of Authorization (LOA).
About 15-20 years ago, in an effort to reduce the regulatory burden on both the FAA and pilots they moved to a process that more closely aligns with type ratings. It is managed under the Vintage & Experimental Aircraft Program.
The stated coverage of the program is:

This program standardizes pilot certification in the following U.S.
aircraft:

Vintage Type Certificated aircraft which require a type rating
Experimental turbine-powered aircraft
Experimental aircraft with a maximum gross weight in excess of 12,500 pounds, or
Experimental piston powered aircraft with an engine over 800 HP and a Vne (never exceed speed) greater than 250 knots

The T-28 falls under the last bullet as it has more than 800 hp.


text:
What is the ratio of Commercial + ATP pilots with employment as pilots in the US?
Of all certificated commercial/ATP pilots in the US under the age of 65, how many are employed in full-time pilot roles vs commercial/ATP pilots with some other profession than a pilot?

Commercial pilot here. I do not fly professionally nor do I want to. A good friend of mine is in the same boat. So...at least two commercial pilots do not fly professionally.

You can find the full database of FAA information at this link but more useful they offer some statistics here.
As of 2018 there are 162,145 individuals that carry an ATP level ticket and 99,880 Commercial tickets out there.
The Bureau of Labor Statistics provides some employment stats however their stuff only goes up to 2016. As of then they claim there are 124,800 jobs for the title "Airline and Commercial Pilots" If we look back at the FAA's 2016 data we will see that in 2016 there were 157,894 ATP tickets out there and 96,081 Commercial level tickets. Assuming that BLS rolls up quite a bit under "Airline and Commercial Pilots" including 135 ops, flight instructor and full on 121 jobs there are 124,800 jobs for 253,975 possibly qualified people.
So there are roughly 129,175 people with ATP or Commercial level tickets not working in ATP/Commercial Aviation jobs.
Note: This does not account for people over 65 (data that it does not appear is released) as well as people who may have lost their medical or otherwise cant fly. However the FAA uses the phrase "ESTIMATED ACTIVE"  which could mean they account for all the above noted things.

The FAA's definition of "active" is a current medical certificate, which is not perfect but probably they best they can do without polling.


text:
Are magnetic compass acceleration errors due to the southern side of the compass being weighted?
When I was in college, I had an instructor who taught me that the acceleration errors in a magnetic compass were due to a counter-weight installed on the south-facing side of the compass that was intended to counter-balance the magnetic dip on the northern side.
It makes sense that this would reduce or prevent north/south-facing turning errors, and would also create acceleration errors while facing east or west.
For example, flying east the weight would be on the right, south-facing side, of the compass, which is the side labeled as 'N'.  Now imagine a straight line acceleration...
The heavier, right side, would move rearward in relation to the aircraft due to its inertial lag, bringing the, weighted, southern side of the compass (which reads north) closer to the compass window causing the viewed indication be a number closer to north, making the "accelerate north" error, true.
The thing is, I have never seen this explanation on paper, just that it is "magnetic dip" error.  Is it true, and can you find a source that says so, or was my professor wrong?

None of my private pilot training, or instrument training, mentioned having weights. They did train us on leading and lagging turning effects, and the effects of acceleration and deceleration.    You can see these yourself by taking a normal camping compass, which is clearly not weighted, and play with turning and accelerating in your car.    https://en.wikipedia.org/wiki/Magnetic_dip  https://en.wikipedia.org/wiki/Compass#Compass_balancing_(magnetic_dip)

"This same idea also holds true for the north and south (Lead North, Lag South) turning errors because the weighted side of the compass would basically fall to the direction of bank." - In a coordinated turn, objects don't fall toward the lowered wing, because gravity and centrifugal force balance each other out. (You still feel a vertical force from gravity and centrifugal force, just not a lateral force.)

@SophieSwett you're right.  I made the correction. Thanks!

I found a source in the old version of the Instrument Flying Handbook, page 3-14 that says, "In acceleration error, the dip-correction weight causes the end of the float and card marked N (the south-seeking end) to be heavier than the opposite end" (ASA-8083-15A).
However, the current copy hosted by the FAA does not have this same wording under the acceleration error section (ASA-8083-15B).
I do not have any reason to believe that the simple magnetic compass technology has changed significantly in the past 10 years, so it looks like it is true that the north-labeled side of the compass card is indeed heavier than the south-labeled side.
This weight is intended to mitigate the north/south turning errors, but is the cause of the acceleration errors.
Old FAA IFH

Current FAA IFH

A third, yet less official, source that corroborates this information is here.

Some compasses are counterweighted to decrease magnetic dip. Older and/or cheaper compasses for land navigation are this way. Many to most are not weighted, especially in aviation compasses. Weighted compasses would require different compasses for the North and South hemispheres. Instead, aviation wet compasses are built with the low friction mounting point above the CG and magnetic bar. This causes the CG to move to the South polarity end of the compass assembly when the magnetic bar dips downward to the North Pole and to the North polarity end when dipping towards the South Pole. I like this article that explains this phenomenon.
Several decades ago, my unit had the opportunity to train with the Australian 3rd Para Regiment in Australia. Many of us had been using personally owned GI lensatic compasses because the tritium markers worked better than the newer, issued lensatic compasses. We were warned that the older models may not be accurate down under due to them being Northern Hemisphere compasses instead of the universal ones. I did not understand the reasoning for this until many years later.

There are no weights added. But the key piece of knowledge is that your compass needle (or the sensing magnets inside the @compass') does not lie on the horizontal, except at the Equator.
Due to the dip of the Earth's magnetic field, your compass/sensing magnets will be slightly nose-down in the Northern hemisphere, and slightly tail-down in the Southern hemisphere. This offsets the CG of the needle/magnets, which gives the appearance of having weights added to a horizontal needle (that isn't horizontal!).
If you now accelerate/decelerate on an Easterly/Eesterly heading, then the offset CG will lag slightly, giving the appearance of a turn. And on a Northerly/Southerly heading, if you bank the airplane the needle/magnets can align themselves with the dip in the Magnetic Field.

The old copy of the handbook I mentioned definitely says there are weights.

What people who say there is not weight are trying to tell me is that acceleration is causing the compass card to "teeter-totter" and tilt and that slight tilt causes a dip effect.  While that would make sense if it were tilting, I don't think it does beyond a negligible amount.  When you accelerate/decelerate, you see no significant tilting in the compass card, and the minor tilting you do see is not commensurate with the amount of card swing, so it stands to reason that its primarily because of a weight imbalance causing interial lag, not because of tilt-dip.


text:
Where are US FIS-B UAT ground facilities located?
In the US there are Flight Information Services Broadcast (FIS-B) transmitters strategically located to provide WX, NOTAMS and other flight information utilizing the ADS-B infrastructure. ADS-B has two physical layers, being the Universal Access Transceiver (UAT) and a 1090 mHz Extended Squitter (1090 ES). FIS-B utilizes the UAT, which are located at 978 mHz.
These UATs are intended for ADS-B use, as well as FIS-B, and additionally Traffic Information Service (TIS-B). They are primarily designed to service traffic below FL180. While they are not deployed to cover all locations, some design goals of the system include having CONUS enroute coverage.
The FAA publishes a coverage map, however, it has apparently not published a list of ground UAT sites. It would be possible to scrape UAT sites and develop a database of ground facilities, however, no one has published the results of doing so, at least that I am aware of.
Having such a list would be helpful to operators such as pipeline, geophysical, agricultural and other operators who tend to fly low, yet may still wish to have FIS-B (and perhaps TIS-B) services, or at least predict where they might be available.
Furthermore, the FAA has said that there is no security provision restricting the disclosure of UATs for FIS-B.  However, they have declined releasing a list of such ground facilities.
Where are the FIS-B UAT ground facilities, and has anyone compiled a list and published it for general access?

Link to the FAA coverage map: https://www.faa.gov/nextgen/programs/adsb/coverageMap/

AIM 2018 7-1-11 helpfully tabulates the service available from different tier towers, but, as pointed out, there is no publicly published list of facilities to help predict when which "tier" of tower will be available.  When that becomes available, I want to know about it.

The FAA does publish a list of towers but no locations, only a generic coverage map.
However, the towers do broadcast their own location, and some Stratux users have collected that data and turned it into a map.

Thanks for the map link.  Limited testing locally shows it to be reasonably accurate.

John Collins on the Beechtalk forums crowdsourced a list of the tower locations a few years ago. It may not have been complete then and there may be more now, but it's a good starting point: https://www.beechtalk.com/forums/viewtopic.php?f=21&t=82540